Oscillograph galvanometer



Aug. 2, 193s. E GERLACH www OSGILLOGHAPIIV GALVANOMETER Fild July 25. 19:56

` s//wu 7.3 MIXER 19M@ CURRENT Erwim Gr Ch r" INVENTUM Patented Aug. 2, 1938 OSCILLOGRAPH GALVAN OMETER Erwin Gerlach,y Berlin-Siemensstadt, Germany, assignor to Klangiilm G. m. b. H., Berlin, Germany, a corporation of Germany Application July 23, 1936, Serial No. 92,086 p In Germany September 24, 1935 3 Claims. (Cl. 171-95) and has for its principal object the provision of an improved impulse recording device which is 5 responsive both to the signal impulses and to a current which varies as the envelope of these impulses. It is an improvement on the recording device disclosed by my copending application, Serial No. 34,930, filed August 6, 1935 and relates more particularly to the provision of means whereby the device of the aforesaid application may be more readily adjusted and operated.

As set forth in the aforesaid copending application, it is customary to produce variable area or variable density sound records by means of electrodynamic sound recording apparatus designed to minimize background noise. Such apparatus includes a conductor to which is supplied both an audio current which varies in accordance with the sound to be recorded and a rectified audio current component which varies as the intensity or volume of such sound.

IThis arrangement is disadvantageous because the direct or rectified current tends to raise the thermal load or stress of the electrodynamic system and for the reason that the resistance of the electrodynamic system is extremely low and the current required to cause a shift in the zero line corresponds only to a small fall of potential across the terminals of the electrodynamic system. This is undesirable on the ground that the D. C. must be obtained from the microphone currents by way of amplification and rectication, and that the tubes used in connection therewith present always an internal resistance which is high in contrast with the resistance of the electrodynamic system. The result is that the D. C. energy in major part is consumed in the last tube and becomes utilizable only in minor part in the electrodynamic system. For the A. C. power which is supplied to the electrodynamic system, the conditions are more favorable in that the insertion of a transformer between the last amplifier tube for the voice alternating voltage and the sound recorder device arrangements'inay be m de so th t the sa'd 1 st tub ur ish a a 1 a e f n es a the tilting of the mirror II in response to variacomparativelyhigh voltage and a correspondingly low current.

As will hereinafter appear, the apparatus functions substantially in such manner that the central position of the oscillation of the electrodynamic system excited in accordance with the sound oscillations to be recorded, is mechanicallyA controlled by' a dynamic system in accordance with the desired displacement of the zero line.

The invention will be better understood from the following description when considered in con-V nection with the single figure of the drawing and its scope is indicated by the appended claims.

An example of an embodiment of the invention '5 is shown in the drawing. In a constant magnetic field produced by the magnet 22 a U-shaped wire I0 is placed. At the ends of the wire II), terminals I3 `and I4 are provided. The wire I0 is held in place by claws I2, furthermore it is maintained 10 in an outstretched position at its bent portion by means of a sheet metal strip I6 whose one end is formed into a hook I5. 'Ihe other end 26 of the strip I6 is connected to a part I1 through a spring 2|. The part I1 can be swung about a shaft 23 15' in the, direction of arrows A. The sheet metal strip IB has fastened thereto a coil 20 having connection terminals 24. The coil 20 is situated in 4the constant -magnetic eld of a magnet 25. The wire has a mirror II mounted thereon. 20 As pointed out in McDowell Patent 1,855,197, the source of signal impulses might be a microlphone from `which the impulses to be indicated are supplied through an amplifier, a mixer, and

an amplifier to the loop Il) of the galvanometer, 25

a part of the signal impulses being supplied through suitable amplifiers to a rectifier and the output of the rectifier being supplied through a D. C. amplifier to the coil 20 which is subjected to themagnetic eld of the magnet 25. 30

The device operates in the following manner:

The sound currents are conducted to the wire IU through` the terminals I3 and I4. Owing toV the constant magnetic'fleld of the magnet 22, the

wire moves in the rhythm of the sound currents. 35 The zero position of the mirror II can be easily adjusted to by moving the part I1 about the shaft 23.

To displace the zero line, the direct `current obtained through detection of .the sound currents 40 is applied to the terminals 2| of coil 20. Hence, the coil 20 moves in the constant magnetic field of magnet 25 therebydisplacing the zero line of mirror Il.

As pointed out in Robinson Patent 1,854,159,

tion in the current of the coil 2U has the effect of bringing the peaks of the low and high frequency impulses more nearly in alignment, so that a minimum of transparent record track area is maintained atvall times. Otherwise stated, the zero lin of the record is shifted in accordance with the impulse level so that the low and high amplitude impulse peaks approach but do not overshoot the edge of the record track area.

I claim as my invention: v

1. A galvanometer including means movable in accordance with impulses to be indicated, a support for said means, means operable to shift said support in accordance with a current which varies as the envelope of said impulses, and means for adjusting the zero position of said support.

2. A galvanometer including means movable in accordance with impulses to be indicated, a support for said means, means operable to shift said support in accordance with a current which var-y accordance with impulses to be indicated, a support for said means, means operable to shift said support in accordance with a current which varies as the envelope of said impulses, a coil mounted on said support, and means for subjecting said coil to a magnetic field of force, means for ad- 10 justing the zero position of said coil.

ERWIN GERLACH. 

